Piezoelectric drive

ABSTRACT

A piezoelectric drive that is used to create a relative movement between a first and a second body on a plane of movement. The drive includes a flat metal sheet ( 1 ) that forms, or is secured to, the first body and that is arranged parallel to the plane of movement. The metal sheet ( 1 ) has a rest region ( 3 ) and at least one resonator area ( 4 ). An elastic spring area ( 5 ), which is parallel to the plane of the metal sheet, is disposed between the rest region ( 3 ) and the resonator area ( 4 ). A flat, rectangular piezoelement ( 6 ), which can be excited in a 3,1 mode, is coupled to a longitudinal axis (A) such that the longitudinal axis of the piezoelement ( 6 ) lies essentially on a longitudinal axis of the resonator area ( 4 ). The resonator area ( 4 ) protrudes above the piezoelement ( 6 ) in the direction of the longitudinal axes (A), and forms a tapered horn shape ( 7 ). The second body ( 2 ) is positioned relative to the sheet metal ( 1 ) such that the at least one resonator area ( 4 ), with an edge area that is disposed at the top of the horn shape, is pressed against a surface ( 10 ) of the second body ( 2 ), which is oriented in an essentially oblique manner relative to the plane of the sheet metal ( 1 ), by prestressing the spring area at a point of contact.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a piezoelectric drive and,more particularly, toward a piezoelectric drive for producing a relativemovement in a movement plane between a first body and a second body.

2. Description of Related Art

Piezoelectric drives, that is to say drives by way of piezoceramicmaterials that may be mechanically changed by an electrical voltagefield, are suitable in particular for miniaturized applications, forexample for motors with a motor volume of a magnitude of a few cubiccentimeters or even with a volume that is smaller than one cubiccentimeter. Further advantages of these drives are high torque at lowspeeds, simple controllability, smooth running, relatively simpleconstruction, and their insensitivity to external magnetic fields aswell as the fact that they themselves produce no magnetic fields.

Piezoelectric drives of the so-called standing-wave type comprise, as adriving element, at least one resonator, which usually consists of apiezoelement and a resonance body (horn) mechanically coupled to thepiezoelement, wherein the piezoelement and the resonator body arematched to one another and the piezoelement is driven such that theresonator oscillates in a standing wave. The horn comprises a taperingfree end that points away from the piezoelement and that advantageouslylies on a point of the greatest oscillation amplitude. It appears thatsuch horn tips, if they are pressed in a suitable manner against amovable body, may drive the movable body in a directed manner, whereinthe force transmission is essentially based on a friction fit.

Such a drive is described in “Piezoelectric Actuators and Ultrasonicmotors” of Kenji Uchino (Kluwer Academic publishers, Boston, Dordrecht,London 1997). This drive comprises a pair of disk-like piezoelementsarranged coaxially over one another that are operated polarized in theopposite direction in a 3,3 mode. A horn connects essentially coaxiallyto the piezoelements. The horn tip is pressed against the surface of abody that is movably arranged parallel to this surface. It has beenshown that the body may be driven in a directed manner with the help ofthe horn if the axis of the horn is not directed exactly perpendicularlytowards the surface but forms a small, acute angle with theperpendiculars to the surface. If the resonator arranged in such amanner is operated at an eigenfrequency, it drives the body in thatdirection in which the slightly oblique horn tip points. The induced,directed movement of the driven body is explained by ellipticaloscillations of the horn tip in a plane perpendicular to the surface ofthe body. A reversal of the movement direction is achieved by areorientation of the resonator axis.

A similar piezomotor is described in the publication DE-3920726 (OlympusOptical). In place of the resonator of the motor described brieflyabove, which is symmetrical to its axis, the motor according toDE-3920726 comprises an asymmetrical horn whose tapering end does notlie on the resonator axis. The resonator is arranged with the axisdirected perpendicularly to the surface of the body to be driven andwith a suitable shaping of the horn tapering towards the horn tip,likewise results in a directed movement of the body created by anelliptical movement of this horn tip. At the same time there areoscillation conditions at frequencies different from one another thatproduce movements in opposite directions. The movement direction maythus be set via the frequency driving the piezoelements. The drive issuggested for application as a linear drive or as a rotational drive,wherein the resonator axis is aligned perpendicular to an end-face ofthe rotor (axially) or perpendicular to the outer surface of the rotor(radially).

The piezoelectric drive according to DE-3920726 may be realised withrelatively simple means as a rotation motor with an end-face drive. Inthe embodiment with the end-face drive it is also possible with simplemeans to mutually pretension the rotor and resonator. It is indeedparticularly these embodiment forms with an axially directed resonatoraxis that have their limits with regard to miniaturization, and onewould like to go beyond these limits.

For motors that are to be very flat, in particular in the axialdirection, it is therefore suggested (e.g. in EP-0505848, ETA SA) to usea centrally arranged, circular-disk-shaped piezoelement that may bedriven in a planar mode. This piezoelement is coupled to a flatresonance body, which is arranged coaxially to the piezoelement andwhich comprises a plurality of asymmetrical horn tips extending radiallytowards an outer ring. Driven by the piezoelements, the horn tips againoscillate in elliptical movements by way of which the outer ring isrotatingly moved about the resonator in a directed manner. The describeddrive, although being able to be designed very thin in the axialdirection, however has always an outer rotor. A pretension between theresonance body and the outer ring is not possible so that the drivereacts very sensitively to wear on the horn tips and the force able tobe transmitted by friction remains limited.

SUMMARY OF THE INVENTION

The present invention is directed toward a piezoelectric drive that maybe realised with the simplest of means, in particular in the case thatits axial extension (or generally: its extension perpendicular to aplane of a movement to be produced) is to be in the range of amillimeter or less. The piezoelectric drive according to the inventionis to be applicable as a linear drive or as a rotation drive, inparticular as an inner rotor.

The piezoelectric drive according to the invention serves for producinga directed, relative movement between two bodies. It comprises a flatdrive plate that forms one of the two bodies or is rigidly connected tothis body and that extends completely flat in one plane that is parallelto the plane of the movement to be created (for a rotational movementthe drive plate is aligned perpendicular to the rotation axis). Thedrive plate forms a rest region on which at least one resonator regionis integrally formed, wherein between the rest region and the resonatorregion there lies a narrow spring region that is resilient in thedirection of the planar extension of the drive plate and that representsan integral component of the drive plate. The drive plate advantageouslycomprises a plurality of resonator regions with spring regions.

A thin, rectangular piezoelement extending parallel to the drive plateand preferably able to be operated in a 3,1 mode is coupled, preferablystuck on the resonator region at least on the one side of the driveplate. The piezoelement has a length that is larger than its width,wherein its length and its width are significantly larger than itsthickness. The two surfaces of the piezoelements extending transverselyto the thickness are designed as contact surfaces. The longitudinal axisor the transverse axis of the piezoelement lies essentially on one axisof the resonator region. In the direction of at least one of these axesthe resonator region projects beyond the piezoelement at least on oneside where it forms a horn or double horn tapering asymmetrically to theaxis. The piezoelement and the resonator region are matched to oneanother such that together they form a resonator which, by way ofpolarization of the piezoelement with a high-frequency alternatingvoltage, may be brought into a condition oscillating in a standing wave.

The two bodies to be moved relative to one another with the help of thepiezoelectric drive according to the invention, of which the first isthe drive plate or is rigidly connected to the rest region of the driveplate, are arranged such that the horn or double horn of the resonatorregion is in contact with a surface of the second body, said surfacebeing aligned essentially transversely to the drive plate, andspecifically such that the slightly pretensioned spring region pressesthe resonator region against the second body, and advantageously suchthat the longitudinal axes of the piezoelement and the resonator regionare aligned essentially parallel or tangentially to the movement to beproduced. The edge region of the drive plate, which is in contact withthe second body (to be driven), is located directly at the horn tip orbetween the tips of the double horn and is advantageously alignedessentially parallel to the longitudinal axes of the piezoelement andresonator region.

Apart from the function of producing a pretension between the two bodiesto be moved relative to one another, the spring region of the driveplate also has the task of decoupling the vibration produced by thedriven piezoelement from the rest region of the drive plate.

It appears that the horn tip of such a flat resonator region givenexcitation by way of the piezoelement at a resonance frequency carriesout elliptical movements in the plane of the drive plate from whichthere results the directed relative movement between the two bodies. Italso appears that there are resonance conditions with a first movementdirection and other resonance conditions with a second movementdirection opposite to the first movement direction.

The elliptical movements of the horn tip may be understood as asuperimposition of the longitudinal oscillation in the direction of thelongitudinal axes of the piezoelement and resonator region withtransversal oscillation in the direction of the width of thepiezoelement, wherein the transversal oscillation propagates into thehorn as bending oscillation. On the other hand a directed bendingoscillation is to be expected by way of an asymmetrical design of thehorn.

It appears that an arrangement in which the longitudinal oscillationruns essentially parallel to the movement direction or parallel ortangentially to the surface to be moved runs more smoothly and with ahigher efficiency with respect to an essentially perpendiculararrangement, which may be explained by the weaker impacts perpendicularto the surface to be driven.

If in each case an equal piezoelement is coupled on both sides of theresonator region, and the two piezoelements are polarized oppositely toone another, then oscillations of the piezoelement in the direction ofits thickness hardly effect the resonator region so that no energy islost by friction on movement of the horn tip transverse to the movementdirection.

The drive according to the invention may be used as a drive for a linearmovement as well as for a rotational movement. Advantageously, aplurality of resonator regions operated in parallel with in each caseone piezoelement or in each case a plurality of piezoelements isintegrally formed on one drive plate. For producing a rotationalmovement the drive plate is arranged transversely to the rotation axisand its rest region for example has the form of a ring on which theresonator regions are integrally formed at regular distances to theinside (inner rotor) or to the outside (outer rotor). For the drive of alinear movement the rest region of the drive plate extends with aplurality of resonator regions essentially in the direction of movement.

For the electrical polarization of all piezoelements arranged on a driveplate, the drive plate may be exploited as the one of the two electricalterminals if the drive plate consists of an electrically conductivematerial and the piezoelements are assembled thereon with anelectrically conducting adhesive. A very simple supply results if twoidentical drive plates are used and the piezoelements are arrangedtherebetween and supplied via the two drive plates. With such anembodiment form one may supply all piezoelements with only twoelectrical connections to the two electrically conducting drive plates,which in particular is advantageous for the smallest designs of thepiezoelectric drive. In order, with an embodiment with two drive plates,to prevent oscillation of the horn tips in the direction of thethickness of the drive plate and/or to use the oscillation for thedrive, it is advantageous to connect the horn tips of each resonatorregion of the two drive plates via an electrically insulating spacer orto provide a groove in the second body to be driven, in which the horntips engage. The mentioned spacer may also assume the function of thefriction partner with the body to be driven.

The drive plate advantageously consists of a good heat-conductingmaterial and is large enough to conduct away heat arising on vibrationin the piezoelements.

The material of the drive plate and its thickness are to be matched tothe piezoelement such that the spring properties of the piezoelement andthe resonator region are matched to one another as well as possible.With an equal width of piezoelement and resonator region the thicknessof the drive plate is to be selected such that the product of thicknessand modulus of elasticity for the piezoelement and the resonator regionis equally large.

The material of the drive plate should furthermore act as little aspossible in a damping manner and have a sufficient mechanical strength.Since the force of the drive according to the invention is transmittedto the body to be moved via friction, the pairing of material betweenthe body to be moved and the drive plate is to be selected accordingly.Where appropriate, the edge region of the resonator region that is infriction contact with the body to be driven may consist of a materialthat is more suitable for the force transmission via friction than therest of the drive plate, or between two drive plates a spacer of such amaterial may assume the friction function.

It has been shown that phosphor bronze is particularly suitable as amaterial for the drive plate. Phosphor bronze has a modulus ofelasticity that is roughly twice as large as the modulus of elasticityof commercially available piezoelements. Thus, with a piezoelementhaving a thickness of 0.5 mm a resonator region of a 0.25 mm thickphosphor-bronze plate or two such resonator regions arranged on bothsides of the piezoelement each with a thickness of 0.125 mm may bedriven. Or, with two such piezoelements arranged on both sides one maydrive a 0.5 mm thick resonator region.

The invention thus relates to a piezoelectric drive for producing arelative movement in a movement plane between a first body and a secondbody. This drive comprises at least one piezoelement drivable with ahigh-frequency alternating voltage and a resonator with a horn or doublehorn, said resonator being mechanically coupled to the piezoelement andexcitable by the piezoelement in a standing wave. The resonator isactively connected to the first body. A region of the horn or doublehorn may be pressed against a surface of the second body for directeddriving.

The drive comprises a drive plate, which forms the first body or isfastened on this and which is arranged essentially parallel to themovement plane. The drive plate comprises a rest region and at least oneresonator region, wherein between the rest region and the resonatorregion there is arranged a spring region (integral part of the driveplate), which is resilient essentially parallel to the plane of thedrive plate. A piezoelement is laterally coupled onto the at least oneresonator region. The second body may be positioned relative to thedrive plate such that the at least one resonator region with an edgeregion, which lies at the horn or double horn, is pressed by way of apretension of the spring region in a contact region against the surfaceof the second body, said surface being aligned essentially transverse tothe plane of the drive element, so that this second body may be drivenessentially parallel to this surface.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the invention will be apparent withreference to the following description and drawings, wherein:

FIG. 1 schematically illustrates a linear drive with a drive plate thathas a rest region and two resonator regions (viewing directionperpendicular to the drive plate);

FIGS. 2 a to 2 f are sections through examples of resonators of thedevice according to the invention with a schematically-shown contactingof the piezoelement or piezoelements;

FIGS. 3 a and 3 b are sections through exemplary contact regions ofresonators according to FIG. 2 d with a body to be driven;

FIGS. 4 and 5 are exemplary embodiment forms of a rotation driveaccording to the invention (FIG. 4: inner rotor; FIG. 5: outer rotor);

FIG. 6 illustrates a further embodiment form of a resonator region of adrive plate;

FIG. 7 illustrates a further embodiment form of a drive according to theinvention with a resonator with a double horn;

FIGS. 8 and 9 are two exemplary motors, which each have more than onedrive according to FIG. 6; and,

FIG. 10 is a schematic operating curve of a drive according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary embodiment form of a piezoelectric driveaccording to the invention, which is designed as a linear drive (viewingangle perpendicular to the movement direction and perpendicular to thedrive plate). The figure shows a drive plate 1, which represents a firstbody or is fastened on such, and a second body 2, which by way of thedrive is to be moved relative to the first body 1 in the one or theother arrow direction. The drive plate 1 comprises a rest region 3 andtwo resonator regions 4, wherein the resonator regions 4 connect to therest region 3 via in each case one spring region 5.

In each case one (where appropriate two) rectangular, flat piezoelements6 are stuck onto the resonator region, wherein the longitudinal axes ofthe resonator region and the piezoelement lie over one another(longitudinal axis A). The resonator region 4 has roughly the same widthas the piezoelement 6 (extension transverse to the longitudinal axis A)and projects beyond the piezoelement 6 in the direction of thelongitudinal axis A on one side where it forms a horn 7 taperingasymmetrically to the longitudinal axis.

The resonator regions 4 are arranged such that the longitudinal axes Aare aligned essentially parallel to the movement direction (doublearrow) and such that a contact edge region 8 directly at the tip of thehorn 7 is pressed against a surface 10 of the second body 2, with thesurface 10 being aligned essentially perpendicular to the drive plate 1.The pressing force is produced by an elastic deformation of the springregion 5 in the plane of the drive plate 1.

The spring region 5 is designed as a narrow strip whose alignmentcomprises a component parallel to the longitudinal axes A and acomponent perpendicular thereto. It opens out advantageously into theresonator region at a location at which a wave node is located forfrequencies at which the drive is to be operated.

It has been shown that resonators as they are shown in FIG. 1 have driveplate thicknesses and piezothicknesses below 1 mm and planar extensionsof less than one cm² for the application of usable resonant frequenciesbetween about 20 and 1000 kHz and that movement directions opposite toone another occur at different frequencies.

FIGS. 2 a to 2 f show exemplary cross sections (perpendicular to thelongitudinal axis) through a resonator (piezoelement 6 as well as aresonator region 4 and a part of the spring region 5 of the drive plate)of the piezoelectric drive according to the invention, as well as veryschematically, a few possibilities for contacting the piezoelement 6 orthe piezoelements 6.

FIGS. 2 a and 2 b show a resonator with a piezoelement 6 coupled ontothe one side of the resonator region 4. The piezoelement is contacted onthe one side via the resonator region 4 to which it is stuck, forexample with an electrically conducting adhesive. The spring region 5 atthe same time serves as a strip conductor, which connects thepiezoelement to a current source or to ground. The other side of thepiezoelement 6 is contacted, for example via a bonding wire 20 or abonding film, wherein the bonding wire 20 advantageously is connected tothe contact surface of the piezoelement at a location representing anode point of the standing wave. The bonding wire 20 is connected to thecurrent source or ground via arbitrary further conductors (FIG. 2 a),e.g. as represented in FIG. 2 b via a strip conductor 21 that runs onthe spring region 5 and that, for example, is formed as a flexprintstuck onto the drive plate in an insulating manner.

FIG. 2 c shows an embodiment form with two piezoelements that arecoupled lying opposite one another on the resonator region 4. Thecontacting is effected, for example, on the one hand via the springregion 5 and the resonator region 4 and on the other hand via stripconductors 21 and bond wires 20 lying on both sides of the spring region5, as is described above for FIG. 2 b.

FIGS. 2 d and 2 e show resonators with a plurality of essentiallycongruently arranged resonator regions 4 of different, advantageouslylikewise congruent drive plates. With this in each case one piezoelement6 is arranged between two resonator regions 4. The contacting of eachpiezoelement 6 is effected advantageously via the resonator region 4 ineach case coupled to the piezoelement. Embodiment forms of resonatorswith several resonator regions 4 or drive plates, which are arrangedcovering one another and in which piezoelements 6 are arranged betweenresonator regions 4, have the advantage of a high stabilityperpendicular to the drive plates, which advantageously consistcompletely of an electrically conductive material and via which, withonly in each case a single connection to the rest region of the driveplate, a plurality of piezoelements of different resonators may becontacted.

FIG. 2 f shows a resonator as in FIG. 2 d, which comprises two resonatorregions 4 and a piezoelement 6 arranged between the resonator regions 4.The piezoelement 6 for its connection to the current source and groundis contacted via the two spring regions 5 and resonator regions 4. Onthe side of the piezoelement that is not applied to ground one taps offa voltage (measuring connection 22), which may serve as a measuringelement of a control for the supply voltage and/or supply frequency.With this, the measuring connection is to be electrically insulated fromthe supply, which means the contact layer of the piezoelement 6 is to beinterrupted around the measuring connection.

FIGS. 3 a and 3 b show sections through contact edge regions 8 ofresonators according to FIG. 2 d that comprise two essentiallycongruently arranged resonator regions 4 or drive plates and apiezoelement 6 arranged therebetween. The contact edge region 8 is thatedge region of the resonator region 4 of a drive plate that is in director indirect contact with the body 2 to be driven.

FIG. 3 a shows a contact edge region 8 in which a distance element 8 isarranged between the resonator regions 4 such that it is not the edgesof the resonator regions which are directly in contact with the body 2to be driven, but rather the distance element 8′. The distance element8′ is to be designed for a sufficient friction on the body to be drivenand for an electrical insulation of the two resonator regions 4 from oneanother. By way of the distance element 8′ oscillations of the resonatorregions 4 transverse to the drive plate and the friction without use tothe drive that this entails is prevented.

For resonators with more than two congruent resonator regions andpiezoelements (FIG. 2 e) arranged therebetween, distance elements areadvantageously arranged in each case between two neighbouring resonatorregions.

FIG. 3 b in the same manner of representation as FIG. 3 shows a sectionthrough a contact edge region 8 of a resonator with two congruentresonator regions 4 in which the resonator regions 4 engage into agroove 8.1 of the body to be driven and are pressed against the base ofthe groove. The groove walls are dimensioned such that they contact theresonator regions in the rest condition. It has been shown that in suchan embodiment form one may transmit more force than with embodimentforms without a groove. This is evidently due to the fact that theoscillations directed transversely to the resonator regions are directedand may be used for the drive.

FIG. 4 shows a further, exemplary embodiment form of the piezoelectricdrive according to the invention that is designed as a rotation driveand specifically as an inner rotor. The drive plate 1 (or whereappropriate a plurality of essentially congruent drive plates), which isfastened on a stator by suitable means, comprises an annular rest region3 and four resonator regions 4, which are directed towards the inside ofthe ring and which are integrally formed on the rest region 3 via springregions 5. The drive plate 1 is arranged perpendicularly to the rotationaxis B of a rotor (second body 2). The resonator regions 4 areessentially the same as those shown in FIG. 1. They comprise in eachcase one essentially straight-lined edge directed towards the rotor, ofwhich a part in the region of the horn tip (contact edge region 8) is incontact with the rotor (where appropriate via a distance element). Thespring regions 5 for example are likewise narrow, straight strips thatare aligned in one direction with a tangential and radial component.

The rotor 2 is not only driven by the resonator regions 4 of the driveplate 1 but also held in its radial position. For certain applications,then, an additional radial pivot pin is not required.

FIG. 5 shows that the piezoelectric drive according to the invention mayalso be applied as an outer rotor that, however, has radially largerdimensions than the inner rotor of FIG. 3. The shown drive does notdiffer in principle to the drives shown in the FIGS. 1 and 3. The sameparts are provided with the same reference numerals.

FIG. 6 shows a further embodiment form of the spring region andresonator region 4 of a drive plate 1 (or a plurality of congruentlyarranged drive plates). These differ from the embodiment forms of theprevious figures by a shape that projects equally beyond thepiezoelement 6 on both sides (two horns 7) and by the shape of thespring region 5.

The projection beyond the piezoelement 6 on both sides gives theresonator region 4 a symmetrical shape relative to the transverse axis Bsuch that standing longitudinal waves with an uneven number of wavenodes have an exactly middle wave node. The middle opening of the springregion 5 into the resonator region 4 is directed to this wave node.

The spring region 5, which is again designed as a narrow strip of thedrive plate, has two curves and between these a region that is alignedessentially parallel to the longitudinal axis A.

FIG. 7 schematically and greatly simplified shows a further exemplaryembodiment form of a piezoelectric drive according to the invention,which is designed as a drive for a rotor 2 rotatingly mounted about arotational axis 12 (viewing angle perpendicular to the movementdirection and perpendicular to the drive plate in the direction of theaxis 12). The figure shows the drive plate, which represents a firstdrive body or is fastened on such, and a second body (rotor), which isto be driven by way the drive relative to the first body 1 in the one orother arrow direction. The drive plate 1 here comprises rest regions 3and a resonator region 4, with the resonator region 4 forming a mainresonator region 4.1 and a secondary resonator region 4.2 that arefunctionally connected to one another via a necking. The secondaryresonator region 4.2 is designed as a double horn 13 asymmetrical to thetransverse axis B. The contact edge region 8 lies in the trough 14between the horns. A symmetrical design of the double horn 13 ispossible with a corresponding, e.g. asymmetrical, arrangement of thebody 2 to be driven.

Designs with several actively connected main and secondary resonatorregions are possible.

The spring region 5 is designed as a narrow strip whose alignment has acomponent transverse to the transverse axis Q. It advantageously opensinto the resonator region 4 at a location at which a wave node islocated for frequencies at which the drive is to be operated.

FIG. 8 shows a motor that consists essentially of three drives accordingto FIG. 7. The drive plate 1 or the drive plates of these drives arearranged centrically in a plane about a body 2 to be driven, such thatthis does not compellingly require an external mounting. The three driveplates 1 shown may also be unified into a single drive plate with threeresonator regions 4.

FIG. 9 shows schematically and greatly simplified, a drive with asimple, flat construction. The drive plate 1 or the drive plates eachcomprise two resonator regions 4 that are connected in each case via aspring region 5 to the rest region 3 and that are designed in the samemanner as the resonator regions 4 represented in the FIGS. 7 and 8.

The drives shown in FIGS. 7, 8 and 9 may all be realized with one orseveral, advantageously congruently arranged drive plates 1, which meansthat when cross-sectioned they may have the shapes represented in FIGS.2 a to 2 f.

It is of course possible to design the resonators of a piezoelectricdrive according to the invention with features that are represented, notcombined with one another, in separate figures.

FIG. 10 very schematically shows an operating curve for the driveaccording to the invention. In this the torque M and the impedance Z arerepresented as a function of the drive frequency ν. Such operatingcurves may for example be measured directly at the piezoelement via avoltage measurement (measuring connection insulated from the supply, atthe side of the piezoelement lying at the supply voltage, see FIG. 2 f).The measurements may serve for determining off-line, the frequency to beselected for a desired movement direction or for the on-line control ofthe supply frequency and/or supply voltage. Under the operating curvethe oscillations of a contact edge region of a resonator, said regionbeing in contact with a body 2, are indicated.

In the operating curve shown there are visible two distinguishedfrequencies ν¹ and ν² for which the elliptical oscillation aligned alongthe surface of the body to be driven with directions opposite to oneanother are determined. The two frequencies ν¹ and ν² are characterisedby a maximal torque and maximal impedance. At a frequency ν=0(standstill) the contact edge region is pressed by way of the pretensionof the spring region against the body to be driven (retaining momentM0). Between the two distinguished frequencies one ascertains anoscillation directed essentially transversely to the surface of the body2 to be driven, which has no driving effect, but which howeverrelevantly reduces the moment with respect to the retaining movement(freerun).

1. A piezoelectric drive for producing a relative movement in a movementplane between a first body and a second body, said drive comprising atleast one piezoelement which may be driven with a high-frequencyalternating voltage, and a resonator (4) with a tapering horn (7), saidresonator being mechanically coupled to the piezoelement and able to beexcited by the piezoelement in a standing wave, wherein the resonator(4) is connected to the first body and a region (8) of the horn may bepressed against a surface (10) of the second body (2), wherein the drivecomprises a drive plate (1) that forms the first body or is fastened onthe first body and that is arranged parallel to the movement plane,wherein the drive plate (1) comprises a rest region (3) and at least oneresonator region (4), wherein between the rest region (3) and theresonator region (4) there is arranged a spring region (5) that isresilient parallel to a plane of the drive plate (1), a flatpiezoelement (6) is coupled laterally onto the at least one resonatorregion (4), and wherein the second body (2) may be positioned relativeto the drive plate (1) such that the at least one resonator region (4),with a contact edge region (8) lying in the region of the horn by way ofa pretension of the spring region (5), is pressed against a surface (10)of the second body (2), which is aligned essentially transverse to theplane of the drive plate (1) such that the second body may be driven (1)such that the second body may be driven essentially parallel to thesurface (10).
 2. The piezoelectric drive according to claim 1, whereinthe at least one piezoelement (6) is flat and rectangular and may beexcited in a 3,1 mode, the longitudinal axes (A) of the piezoelement (6)and the resonator region (4) are arranged lying over one another and thehorn (7) extends in the longitudinal direction and the contact edgeregion (8) is aligned essentially parallel or tangentially to themovement direction.
 3. The piezoelectric drive according to claim 2,wherein the horn (7) of the at least one resonator region (4) tapersasymmetrically to the longitudinal axis of the resonator region (4). 4.The piezoelectric drive according to claim 1, wherein the resonatorregion (4) comprises a main resonator region (4.1) and at least onesecondary resonator region (4.2).
 5. The piezoelectric drive accordingto claim 4, wherein the secondary resonator is shaped as a double horn(13) with a trough (14) and the contact edge region (8) is arranged inthe trough (14).
 6. The piezoelectric drive according to claim 1,wherein, on each side of the piezoelement (6) or the piezoelements (6),a resonator region (4) of a drive plate (1) is coupled.
 7. Thepiezoelectric drive according to claim 6, wherein in the contact edgeregion (8) between the two resonator regions (4) arranged in each caseon one side of the piezoelement (6) there is arranged a distance element(8′).
 8. The piezoelectric drive according to claim 1, wherein themovement to be produced is a rotational movement and the rest region (3)of the drive plate (1) is essentially annular.
 9. The piezoelectricdrive according to claim 8, wherein the drive plate (1) comprises aplurality of resonator regions (4) and wherein said plurality ofresonator regions are at regular distances from one another and, on aninward or outward side, connect to the rest region (3).
 10. Thepiezoelectric drive according to claim 1, wherein the spring region (5)is a narrow strip whose alignment has a component parallel to thelongitudinal axes (A) and which opens into the resonator region (4)where a standing longitudinal wave has a wave node.
 11. Thepiezoelectric drive according to claim 1, wherein the drive plate (1)consists of an electrically conducting material, a plurality ofpiezoelements (6) are stuck onto the resonator regions (4) with anelectrically conducting adhesive, and the drive plate (1) in the restregion (3) is connected to the high-frequency alternating voltage or toground.